Zinc base alloy



Patented Jan. 30,1934

ZINC BASE ALLOY Pascal J. Morell, Waterbury, Conn., assignor to TheAmerican Brass Company,

Waterbury,

Conn., a corporation of Connecticut No Drawing. Application July 9, 1931Serial No. 549,804

3 Claims.

This invention relates to a new zinc base alloy of superior strength andpermanence developed more particularly for casting purposes andespecially for die casting purposes.

5 Die casting alloys have been developed within recent years which showconsiderable improvement in physical properties and more particularlysuperior'permanence of size and shape as compared to alloys widely usedin the die casting industry but a few years ago. These newer alloys,

however, require the use of a special zinc of a very high degree ofpurity and consequently extreme care must be used in the preparation andhandling of the alloys in the manufacture of castings therefrom to avoidcontamination.

The new alloy disclosed herein has the special advantage that itcombines high strength with considerable permanence even when made withzinc of less special quality. It is to be distinctly understood,however, that the alloy described herein may be made with zinc of thehighest purity obtainable and that the use of such zinc will add tothose superior properties generally associated with the use of such purezinc. It is intended that this patent shall cover the alloy disclosedwhen the zinc used therein is either of the special high purity grade(99.98+% zinc content) or the more widely used high grade or No. 1 asspecified by the American Society for Testing Materials.

A zinc base alloy commonly in use at the pres-.- ent time contains about4% aluminum, about 3% of copper and about 0.1% of magnesium. In fact acommittee of the American Society for Testing Materials is recommendingan alloy of this composition for adoption as a standard alloy by thesociety.

It is well known that this alloy has the disadvantage that the physicalproperties of tensile strength, elongation and impact strength decreasewith time even at normal atmospheric temperatures and more rapidly atelevated temperatures. This change in physical properties is consideredto be due to a phase change in the alloy. Zinc-aluminum-copper alloys ofthe type represented by the composition 4% aluminum, 3 copper andremainder zinc form a rather complex ternary system which has beenstudied in detail by various investigators. It is considered that due tothe rapid freezing and cooling of alloys in the die casting process thatcasting alloys of the above type are left in a phase of unstableequilibrium and that the alloy consequently tends to change with time tothat form which is stable at normal temperatures. This change involvesthe precipitation within the alloy of a relatively hard and brittlecompound of copperand aluminum. It is the precipitation of this hard andbrittle compound within the alloy that causes the decrease in physicalproperties known to occur in castings with time, that is upon aging.

Study of the ternary equilibrium diagram of zinc-copper-aluminum showsthat the presence of the copper-aluminum compound under equilibriumconditions at normal temperatures is dependent on the ratio of copperand aluminum in the alloy.

Based on these facts and laboratory investigation I have discovered thata zinc base alloy containing from about 15% to about 35% aluminum andfrom-about 0.01% to about 0.2% magnesium has superior physicalproperties to other alloys at present used in die castings. The alloy isimproved in certain respects, particularly by increased tensil strengthand hardness, by additions of small amounts of copper. The aluminum ispreferably from about 20% to about 24% and it is desirable to keep themagnesium as low as possible but sufiicient to prevent inter-crystallinecorrosion. Where copper is added it is preferred from about 0.01% toabout 5%. I have discovered that a zinc base alloy containing around 20%aluminum and about 0.1% magnesium has very superior physical propertiesto other alloys at present used in die castings. The same was found tobe true of a similar alloy containing about 20% aluminum, about 1%copper and about 0.05% magnesium.

I have discovered further that the physical properties especially theductility and impact strength increase with time. I have discoveredstill further that this increase in physical properties may be obtainedand hastened by suitable heat treatment. It is intended that thisbeneficiation of physical properties by heat treatment shall form a partof this patent. I have found that with these alloys by heating forvarious lengths of time depending on the temperature certain improvementin their properties can be secured particularly the ductility and impactresistance, and the higher the temperature the more rapid the efiect upto temperatures slightly below the transformation temperature of thealloy. The maximum temperatures to which the alloy can be heated tosecure this improvement depend in a large measure upon the castingconditions, the design of casting and the composition of the alloy. Thebeneficiation by heat treatment, that is improvement in physicalproperties by heat treatment is very important.

maaese aluminum, about 0.1 percent magnesium, and the remainder zincmetal.

3. A zinc base alloy comprising from about to about 24% aluminum, about0.01% to about 0.2% magnesium, and the balance zinc metal. i

PASCAL J. MORELL.

